In measurement, hole a of the gauge is connected to the inner tube in which the pressure is to be measured. At this, stem 1 contacts piston 2. The pressure in the tube pushes piston 2 to the right, overcoming the resistance of spring 3 and displacing stem 1. When the gauge is disconnected from the inner tube, the pressure in piston 2 drops and spring 3 returns the piston to its initial position. Stem 1, held by flat springs 5, remains in the position it was pushed by piston 2. The measured pressure is indicated on a scale which is inscribed on stem 1 (by the amount of the stem sticking out of cylindrical body 4). Before the next measurement the stem is pushed back into the body. Pin 6 prevents stem 1 from being pulled entirely out of body 4.
$3720$SHP,M$